For an existing lock for a movable door, hook tongues in a prior art are enabled to rotate around a rotating shaft under a direct drive of a connecting rod. Rotation angle of the hook tongues is decided by a moving distance of the connecting rod, for example, as disclosed by U.S. Pat. Nos. 6,264,252B1 and 8,827,324B2, and Chinese patent No. 201420278913.5. When the door leaf has been unlocked and the hook tongues of the lock are exposed, movement of the connecting rod is generally controlled and locked by a relevant mechanism such as an additional button, or the hook tongues are controlled not to extend out of a lock shell, so that the hook tongues are prevented from impacting against passing pedestrians. However, when the button doesn't work or other reasons that make the pair of hook tongues extend out, it is very easy to cause injury to people and result in safety accidents.